That's the real issue at hand here. Scooters are light enough that someone can just buy one and carry it around with them all day. At $5+ a ride, it isn't long before people would rather just buy one of their own.
Bikes are at least large enough to be a hassle to carry around.
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Consider computers (and no, not cloud computers. Like normal office computers). There was a time when timesharing computers was popular, when computers were $100,000.
Similarly, back in high school, one local entrepreneur gave a talk to my school. He explained that 3d printers, while their costs were going down, were still too expensive to own. He predicted 10 years before 3d printers were popular for home labs (and it turns out he was right). In those 10 years, he made money by renting out university-level / research 3d Printers (no one wanted to buy $100,000+ printers anymore, everyone saw the writing on the wall and would rather rent), so the rental company did well, albeit only temporarily. (Overall, the talk was about "risk taking". In this case, the calculated risk that he'd make money before the business opportunity closed as 3d printers became cheaper)
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But these Bird scooters look like they're around $500? If you're using the thing like 2 or 3 times a day, it won't take long at $5 / ride before it makes more sense to just buy one for yourself.